$DF13/57107/MMC+3: Identification Register
On Read: #$64 when Bit 1 of $DF11 is 0
#$01 when Bit 1 of $DF11 is 1 and REV A hardware is used
#$02 when Bit 1 of $DF11 is 1 and REV B hardware is used
On Write: Write #$55 & #$AA into this register to unlock Bit 3 of $DF11
Write #$0A & #$1C into this register to re-enable MMC64 hardware